Hydro-liquefaction of sawdust and its three components in supercritical ethanol with [BMIM]Cl/NiCl2 catalyst

• The [BMIM]Cl/NiCl2 was utilized as a catalyst to enhance biomass conversion and improve the bio-oil yield.
• The supercritical ethanol and ionic liquid nickel catalyst showed synergistic effect on the sawdust hydro-liquefaction.
• The temperature and hydrogen pressure have an influence on the product distributions of sawdust and three components.
• The dominant compositions of bio-oil highly depended on the biomass components.

Sawdust was subjected to the catalytic hydro-liquefaction process in the supercritical ethanol under the experimental conditions (320 °C and 30 min). The maximum sawdust conversion of 69.8% and liquid yield of 49.5% were achieved in ethanol with [BMIM]Cl–NiCl2 as catalyst, indicating that the synergistic effect of supercritical ethanol and ionic liquid nickel catalyst on the sawdust liquefaction. To further understand the hydro-liquefaction behavior of lignocellulose, effect of temperature and hydrogen initial pressure on the liquefaction of sawdust and its major components (cellulose, hemicellulose and lignin) were investigated in supercritical ethanol with [BMIM]Cl–NiCl2 catalyst. The highest bio-oil yield could be obtained at 320 °C under 10 Mpa hydrogen initial pressure. The resulted liquid products were analyzed by gas chromatography–mass spectrometry (GC–MS). The sawdust, cellulose and lignin derived oil mainly consisted of ester and phenolic compounds whereas hemicellulose-derived oil primarily contained aldehyde and ketone compounds. According to the GC analysis, the gaseous products were consisted of carbon dioxide, methane, ethane and ethylene. The ethane was the dominant components from sawdust and the three constituents.